1. Field of the Invention
The present invention relates to an optical disk for recording therein video signal and audio signal, and an optical recording and reproducing apparatus for recording and reproducing video and audio signals onto and from the optical disk.
2. Description of the Prior Art
Recently, the optical disk is noticed as an information recording medium of large storage capacity and fast access speed. Known optical disk recording methods include a constant linear velocity (CLV) method in which the rotating speed of a disk is varied in inverse proportion to the track radius so that the linear velocity of the track may be constant anywhere on the disk, a constant angular velocity (CAV) method in which the disk is rotated at a constant angular velocity, a modified CLV (MCLV) method, and a modified CAV (MCAV) method. The MCAV method is a recording method in which the rotating speed of the disk is kept constant, the recording area is divided into plural regions called zones in the radial direction of the disk, and the clock frequency for recording is varied zone by zone so as to be higher as going closer to the outer circumference so that the recording mark length becomes almost the same at the outer side and at the inner side. In the MCAV method, since the rotating speed of the disk is constant, the control of rotation of the spindle motor for rotating the disk is easy, and the sector position can be specified radially from the center of the disk, so that it is excellent in random access performance. Moreover, since the recording mark length is the same at the inner side and at the outer side the recording capacity can be increased, which improves the defect of shortage of storage capacity in the CAV method.
In the audio-video field, on the other hand, by making use of the excellent random access performance, the optical disk has been applied in an editing machine capable of easily post-scoring or pre-scoring only audio signal or video signal, or only a specific channel among plural channels.
In the MCAV method, however, since the linear velocity is faster and the recording frequency is higher at the outer side as compared with the inner side, the jitter is worsened at the outer side as compared with the inner side, thereby resulting in a difference in the recording and reproducing characteristic.